1. Field of the Invention
The present invention relates to an air conditioner, and more particularly to a method for operating an air conditioner to rapidly and efficiently eliminate a warming load.
2. Description of the Related Art
Generally, an air conditioner is an appliance for cooling or warming a room using a cooling cycle of a refrigerant compressed into a high-temperature and high-pressure state by a compressor.
The compressor includes a compressing unit having a compressing chamber for compressing the refrigerant, and a motor unit for varying the volume of the compressing chamber. In the case of an air conditioner equipped with a plurality of indoor units or a large-capacity air conditioner, a plurality of compressors are used. In association with such an air conditioner, it is possible to reduce the consumption of electric power required to drive compressors by varying the capacity of the compressors in accordance with the load to be eliminated.
FIG. 1 is a schematic diagram illustrating a cooling cycle established in a conventional air conditioner. FIG. 2 is a schematic diagram illustrating a warming cycle established in the conventional air conditioner.
As shown in FIGS. 1 and 2, the conventional air conditioner includes an indoor heat exchanger 2 for heat-exchanging air in a room with a refrigerant, thereby cooling or warming the room, an outdoor heat exchanger 4 serving as a condenser for condensing the refrigerant when the indoor heat exchanger 2 functions as a cooler, while serving as an evaporator for evaporating the refrigerant when the indoor heat exchanger 2 functions as a heater, and first and second compressors 6 and 16 for compressing the refrigerant from a low-temperature and low-pressure gaseous state into a high-temperature and high-pressure gaseous state in order to supply the high-temperature and high-pressure gaseous refrigerant to the indoor heat exchanger 2 or outdoor heat exchanger 4. The air conditioner also includes an expansion device 8 arranged between the indoor heat exchanger 2 and the outdoor heat exchanger 4, and adapted to expand the refrigerant into a low-temperature and a low-pressure state, and a control unit (not shown) for controlling operations of the first and second compressors 6 and 16 in response to an operation of the user and in accordance with the load to be eliminated. The indoor heat exchanger 2, outdoor heat exchanger 4, first and second compressors 6 and 16, and expansion device 8 are connected by a refrigerant pipe 9.
In FIGS. 1 and 2, the reference numeral 24 denotes a common accumulator to which respective suction lines 6a and 16a of the first and second compressors 6 and 16 are connected. This common accumulator 24 serves to store a liquid refrigerant not evaporated by the indoor heat exchanger 2 or outdoor heat exchanger 4, in order to prevent the liquid refrigerant from being introduced into the first and second compressors 6 and 16. Introduction of such a liquid refrigerant into the compressors 6 and 16 may cause failure of those compressors.
Also, the reference numeral 26 denotes a direction change valve, for example, a 4-way valve, adapted to change the flowing direction of the refrigerant in accordance with a control signal from the control unit so that the air conditioning system is used for a cooling or warming purpose. This 4-way valve 26 communicates with the common accumulator 24 and respective discharge lines 6b and 16b of the first and second compressors 6 and 16. The 4-way valve 26 guides the high-temperature and high-pressure gaseous refrigerant compressed by the first compressor 6 or second compressor 16 to the outdoor heat exchanger 4 in a cooling mode, while it guides the same gaseous refrigerant to the indoor heat exchanger 2 in a warming mode.
The reference numerals 32 and 34 are check valves respectively installed in the discharge lines 6b and 16b of the first and second compressors 6 and 16, and adapted to prevent the refrigerant discharged from the currently-operating compressor, for example, the first compressor 6, from being introduced into the currently-stopped compressor, for example, the second compressor 16.
Meanwhile, the first compressor 6 has a capacity of X%, for example, 60%, whereas the second compressor 16 has a capacity of Y%, for example, 40%. Compressor operation is carried out with a capacity of 100%. or X% by operating both the first and second compressors 6 and 16 or operating only the first compressor 6 in accordance with a control signal from the control unit.
Now, the conventional air conditioner having the above described configuration will be described.
When the air conditioner is set to operate in a warming mode under the condition in which a target temperature T0 is set, the control unit first switches the operating position of the 4-way valve 26 to correspond to the warming mode, as shown in FIG. 2, and operates the first and second compressors 6 and 16.
The first and second compressors 6 and 16 discharge a high-temperature and high-pressure gaseous refrigerant which, in turn, passes through the indoor heat exchanger 2. The refrigerant is condensed while discharging heat therefrom around the indoor heat exchanger 2. In this case, the indoor heat exchanger 2 serves as a heater.
The refrigerant condensed into a high-temperature high-pressure liquid state while passing through the indoor heat exchanger 2 then passes through the expansion device 8 which, in turn, expands the refrigerant into a low-temperature and a low-pressure state so as to change the refrigerant into an easily evaporable state. The expanded refrigerant is then sent to the outdoor heat exchanger 4. The refrigerant absorbs heat around the outdoor heat exchanger 4 while passing through the outdoor heat exchanger 4, so that it is evaporated. The resultant refrigerant is introduced into the first and second compressors 6 and 16. Thus, a warming cycle is established.
Once the warming load is substantially eliminated in accordance with the above described operations of the first and second compressors 6 and 16, only the first compressor 6 is repeatedly operated and stopped in order to cope with a subsequent warming load under the condition that the second compressor 16 is maintained in a stopped state.
FIG. 3 is a graph depicting a variation in compression capacity depending on a variation in room temperature in the warming mode of the conventional air conditioner.
When the indoor heat exchanger 4 performs a warming operation in accordance with operations of the first and second compressors 6 and 16, the room temperature T is increased, as shown in FIG. 3. When the room temperature T exceeds an upper temperature limit of T0+xcex94T higher than the target temperature T0 by an allowable temperature deviation xcex94T of, for example, 0.5xc2x0 C., the control unit stops the first and second compressors 6 and 16.
Subsequently, the room temperature T decreases gradually because the first and second compressors 6 and 16 are maintained in a stopped state. When the room temperature T is lowered below a lower temperature limit of T0xe2x88x92xcex94T lower than the target temperature T0 by an allowable temperature deviation xcex94T of, for example, 0.5xc2x0 C., the control unit again operates the first and second compressors 6 and 16.
On the other hand, when the room temperature T again exceeds the upper temperature limit of T0+xcex94T in accordance with the re-operations of the first and second compressors 6 and 16, the control unit again stops the first and second compressors 6 and 16.
After operating the first and second compressors 6 and 16 two times in the above manner, the control unit determines that the warming load is substantially eliminated. Based on this determination, the control unit operates only the first compressor 6 when the room temperature T is again lowered below the lower temperature limit of T0xe2x88x92xcex94T, and subsequently stops the first compressor 6 when the room temperature T again exceeds the upper temperature limit of T0+xcex94T.
Thus, the air conditioner copes with subsequent warming loads by repeatedly operating and stopping the first compressor 6.
Although the warming operation of the conventional air conditioner is carried out in such a fashion that an X% operation is repeatedly and intermittently performed following two 100% operations, there is a problem in that the time taken for the room temperature T lowered after the two 100% operations to again reach the target temperature may be lengthened because the X% operation is achieved only by the first compressor 6, so that the X% operation should be carried out for an extended time.
In order to solve the problem caused by the X% operation, another operating method was proposed. In accordance with this operating method, a 100%/X% operation is carried out by operating both the first and second compressors 6 and 16 at an initial stage of the warming mode, thereby performing a 100% operation, stopping the second compressor 16 during the operations of the first and second compressors 6 and 16, thereby performing an X% operation, and stopping the first compressor 6 when the room temperature T exceeds the upper temperature limit of T0+xcex94T. The 100%/X% operation is repeated when the room temperature T is lowered below the lower temperature limit of T0xe2x88x92xcex94T. However, this operating method has a problem in that the consumption of electric power increases because both the first and second compressors 6 and 16 operate even when the room temperature T can rapidly reach the target temperature by operating only the first compressor in accordance with a substantial elimination of the warming load by the 100%/X% operation repeatedly carried out several times.
The present invention has been made in view of the above mentioned problems involved with the related art, and an object of the invention is to provide a method for operating an air conditioner in a warming mode which is capable of rapidly coping with a warming load while reducing the consumption of electric power.
In accordance with the present invention, this object is accomplished by providing a method for operating an air conditioner equipped with a plurality of compressors in a warming mode by operating a part or all of the compressors in accordance with a warming load to warm air in a room, comprising the steps of: (A) operating/stopping all of the compressors; (B) determining a warming load to be eliminated after execution of the step (A); (C) operating all of the compressors when it is determined at the step (B) that the warming load is not large, subsequently stopping a part of the compressors, and subsequently stopping the remainder of the compressors; (D) determining a warming load to be eliminated after execution of the step (C); and (E) operating/stopping the part of the compressors when it is determined at the step (D) that the warming load is small.